The present invention relates to a multi-television broadcasting signal receiving apparatus and a control method thereof. More particularly, the present invention relates to a multi-television broadcasting signal receiving apparatus and a control method for automatically adjusting the concentration of the color of a television signal to correspond to the broadcasting system of the television signal.
There are several types of commercialized television broadcasting systems for television signals. For example, one commercialized broadcasting system is a National Television System Committee (NTSC) system which was created based on recommendations from the American Television System Committee. Subsequently, other systems were developed which modified the NTSC system but maintained a majority of basic features of the NTSC system. For example, some of the modified systems are the Phase Alternating Line (PAL) system and the Sequential Color with Memory (SECAM) system.
Each of the systems mentioned above have their individual advantages and drawbacks. Moreover, the devices used to detect such broadcasting systems are also different from each other. For example, in the NTSC system, the frequency of the chrominance subcarrier is 3.58 MHz, and the frequency of the vertical synchronization signal (hereinafter referred to as a `vertical frequency`) is 60 Hz. In the PAL system, the chrominance subcarrier wave frequency is 4.43 MHz and the vertical frequency is 50 Hz. Finally, in the SECAM system, the frequencies of two of the chrominance subcarrier waves are 4.40625 MHz and 4.25 MHz, and the vertical frequency is 50 Hz.
Also, each broadcasting system is different with respect to the time at which video and audio signals are detected and with respect to the frequencies of the vertical sync signal and the chrominance subcarrier. In particular, the chrominance level of a broadcasting signal of the PAL or SECAM system is relatively strong when compared to a broadcasting signal of the NTSC system.
Due to the different characteristics of the NTSC, PAL, and SECAM systems, the chrominance level of a video signal varies according to the broadcasting system of the signal. Therefore, a multi-television having the capability of receiving broadcasting signals from each of the above described broadcasting system needs to adjust the chrominance concentration of a video signal in accordance with the broadcasting system of the signal.
An example of a multi-television which has the capability of adjusting the chrominance concentration of a received signal according to the broadcasting systems of the signal is shown in FIG. 1. As illustrated in the figure, the broadcasting signal of an aerially transmitted radio frequency (RF) is received by a tuner 10 via an antenna. Subsequently, the tuner 10 outputs a corresponding intermediate frequency (IF) by mixing the received broadcasting signal with an oscillating frequency signal. The oscillating frequency signal is supplied from a local oscillator (not shown) in accordance with a control signal supplied from a microcomputer 12.
The IF signal is then output to an IF signal processing portion 14 which amplifies the IF signal, produces a corresponding wave form, and outputs the wave form to an NTSC detecting portion 16 and a PAL detecting portion 18. Furthermore, the IF signal processing portion 14 outputs the IF signal to the microcomputer 12.
Since the chrominance level of an NTSC broadcasting signal is lower than the chrominance level of a PAL broadcasting signal, the broadcasting signal output from the NTSC detecting portion 16 is input to a chrominance signal level correction portion 20. As a result, the chrominance level of the NTSC signal is adjusted such that the resultant video image displayed on a picture tube (not shown) has the proper chrominance concentration.
The corrected NTSC broadcasting signal output from chrominance signal level correction portion 20 and the PAL broadcasting signal output from PAL detecting portion 18 are respectively supplied to first and second input terminals of a switch 22. The switch 22 selectively inputs either the corrected NTSC broadcasting signal or the PAL broadcasting signal based on a discrimination control signal output from the microcomputer 12. The microcomputer 12 determines whether the received broadcasting signal is an NTSC signal or the PAL signal according to the frequency of the vertical sync signal of the IF signal received from the IF signal processing portion 14. Therefore, since the vertical sync signal of an NTSC signal is different than that of a PAL signal, the microcomputer 12 is able to determine whether the broadcasting signal is an NTSC or a PAL signal and generates a corresponding discrimination control signal.
Accordingly, the switch 22 selectively outputs either the corrected NTSC signal or the PAL signal based on the discrimination control signal. The output of the switch 22 is then input by a chrominance signal amplifying portion 24 which amplifies the broadcasting signal to a level suitable for displaying the signal. In particular, the broadcasting signal is amplified based on a predetermined gain which is established based on a control signal from the microcomputer 12. Subsequently, the amplified broadcasting signal is output to the picture tube (not shown). Furthermore, even though the chrominance signal is amplified by a predetermined amount, one can also adjust the chrominance level of the signal to a desired chrominance concentration by inputting an appropriate command via a key input portion 26.
As described hereinabove, the apparatus shown in FIG. 1 comprises both a chrominance signal level correction portion and a chrominance signal amplifying portion to properly display both an NTSC broadcasting signal and a PAL broadcasting signal. Accordingly, the cost of manufacturing such apparatus is relatively high since both a correction portion 20 and an amplifying portion 24 are required. Also, the design of the correction circuit is complicated, and the number of hardware components for the apparatus is relatively high.